The present invention relates to an electrical dispersion compensator and a tap coefficient calculation method performed in the electrical dispersion compensator. Specifically, it relates to a technology to successfully perform waveform shaping in a case of a low sampling rate.
In an optical access network that receives a wide variety of service requests from users, traffic demand has been temporally and spatially ubiquitous, so that novel network architecture for highly-efficient network control will be required in the future.
As one example of the network architecture capable of such as providing optimum communication capability and integrating different kinds of services, a WDM/TDM-PON is under consideration, which is configured by adding a wavelength division multiplexing (WDM) technology to a conventional passive optical network (PON) technology based on a time division multiplexing (TDM) technology, and performs waveform shaping according to a traffic usage situation on a network (see, for example, the publication entitled “λ-tunable WDM/TDM-PON using DWBA for flexible service upgrade” by Hirotaka Nakamura et al., 2010, the Institute of Electronics, Information and Communication Engineers, Communications Society Conference, B-10-40).
This technology enables drive control of an optical line terminal (OLT) according to traffic to improve band usage efficiency, so that a center office is expected to achieve low power consumption. The WDM/TDM-PON is aimed at widening a coverage area by capacity enlargement and multi branching, thus requiring OLT integration by extending a transmission distance.
As for a technology to extend the transmission distance, a wavelength dispersion compensating technology is used for coping with a problem of deterioration in waveform due to wavelength dispersion. The wavelength dispersion compensating technology includes an electrical dispersion compensating (EDC) technology (see, for example, JP 2006-287695A). The EDC technology is a technology to correct a signal waveform distorted by the wavelength dispersion by using digital signal processing.
Here, the digital signal processing includes sampling a signal having a deteriorated waveform through transmission, comparing the signal with a signal before the transmission in terms of values at sampling points, and performing waveform shaping so as to bring the values after the transmission close to the values before the transmission. The digital signal processing is conducted by using an equalizer, or the like.